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17046674a7
- neg can only overflow, if a == MIN - case `-0` is properly handled by hardware, so overflow check by comparing `a == MIN` is sufficient - tests: MIN, MIN+1, MIN+4, -42, -7, -1, 0, 1, 7.. See #1290
32 lines
957 B
Zig
32 lines
957 B
Zig
// negv - negate oVerflow
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// * @panic, if result can not be represented
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// - negvXi4_generic for unoptimized version
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// assume -0 == 0 is gracefully handled by the hardware
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fn negvXi_generic(comptime ST: type) fn (a: ST) callconv(.C) ST {
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return struct {
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fn f(a: ST) callconv(.C) ST {
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const UT = switch (ST) {
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i32 => u32,
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i64 => u64,
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i128 => u128,
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else => unreachable,
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};
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const N: UT = @bitSizeOf(ST);
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const min: ST = @bitCast(ST, (@as(UT, 1) << (N - 1)));
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if (a == min)
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@panic("compiler_rt negv: overflow");
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return -a;
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}
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}.f;
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}
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pub const __negvsi2 = negvXi_generic(i32);
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pub const __negvdi2 = negvXi_generic(i64);
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pub const __negvti2 = negvXi_generic(i128);
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test {
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_ = @import("negvsi2_test.zig");
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_ = @import("negvdi2_test.zig");
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_ = @import("negvti2_test.zig");
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}
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